I think if its left at room temp it doesn't last as long as in the freezer. I think its only a few days at room temp and about a month when frozen. I'm not a vet so I don't know if that is precise, but that is what my vet told me when I had to do a round of injections.

What I did though was prep a bunch of syringes all at once and leave those in the freezer so I only needed to take one out when I needed it. Convenient and it thaws much quicker.